Reducing emissions is possible for cement manufacturers like Norcem using SICK’s dust measurement technology
The human eye can’t tell the difference from a water droplet or dust particle. Measuring instruments that specialize in measuring dust concentrations in wet gas help with this. However, not all dust measuring devices reliably control to ensure that the emission limits can be compliant. The exhaust gas after scrubber systems is usually very cold and saturated with water, creating challenges for the measurement technology.
The Norwegian cement manufacturer Norcem— a member of the worldwide group HeidelbergCement — wants to do more for the environment and emit fewer pollutants. To ensure that everything is done in accordance with legal requirements for low limit values, innovative dust measurement devices from SICK are used as a decisive measurement tool after the flue gas scrubber.
Norcem Kjøpsvik, the world’s northernmost cement plant, is remotely located in the Arctic Circle in the middle of the Norwegian remoteness. It’s the only plant within a radius of 1,000 km and it is taking on a remarkable task. Norcem Kjøpsvik produces cement for the domestic market, which is often not easy because many routes surrounding the plant are cumbersome and time-consuming to traverse. Because of the distance alone, the process chain and equipment must function perfectly.
In addition, the sulphureous limestone has caused problems in the past because the Sulphur content was too high, and the plant increasingly exceeded the permitted emission limits. The limestone was extracted from the adjacent quarry and a constructive rethink was needed. Norcem changed its mining plan and extracted low-Sulphur limestone from other areas, but this significantly extended the transport distances and was not a sustainable long-term change, only a temporary solution.
The situation transformed abruptly when Norcem was able to invest in a flue gas desulphurization (FGD) plant based on a seawater scrubber with the support of the state environmental fund. This technology was used to remove SO2 from the flue gas with a high separation rate. This made lime mining in the adjacent limestone quarry possible again. Since then, the dust sensor technology from SICK has been measuring concentrations in the wet gas, helping Norcem Kjøpsvik’s emission limits fall in the green range.
Clean exhaust gas and compliant emission limit values are the cornerstones of success. Luckily, the gas cleaning system was ready for operation in little to no time. The contract with the equipment supplier was signed in Fall 2017, installation work began in Summer 2018, and hot commissioning took place in May 2019.
In the meantime, more than 95% of the Sulphur dioxide was washed out and the maximum SO2 concentration at the stack outlet is limited to < 50 mg/m³, an excellent value.
The plant uses only seawater instead of chemical absorbents, but this does challenge the continuous dust concentration measurement. The difference between a water droplet and dust particle is still unclear and in the wet gas duct it is indistinguishable for standard devices. Inaccurately measured values of such devices are unacceptable for emission reporting. The measurement performance of the dust monitor from SICK, on the other hand, is light years ahead of the standard, because the FWE200DH is designed especially for difficult measurement conditions such as these.
Using a specific design to measure dust
According to the optical principle, the scattered light intensity determines the dust concentration. Disturbing water droplets must be removed before the measurement.
The FWE200DH extracts sample gas from the exhaust gas flow and in the bypass system, the water droplets evaporate so that they no longer hinder the accurate measurement. The exhaust gas flows back into the gas duct after the measurement. The FWE200DH measures in many applications and industries worldwide, but the special installation conditions at Norcem Kjøpsvik were a new challenge for SICK’s particle analyzer team.
The tight geometric space conditions in the mounting flange made the use of a usual measuring gas probe for exhaust gas extraction impossible. For correct functioning, the sample gas probe must be mounted facing downwards, which isn’t possible with a standard probe design and this is easily manageable with a customer-specific probe geometry provided by SICK.
During commissioning, it became apparent that the sample gas probe could be mounted without any problems, and this made it possible to link the functional requirements with the real installation conditions.
Managing chlorine input and carbon dioxide emissions
In addition to the high Sulphur volatiles from the raw material, the high chlorine input from alternative fuels also causes problems in cement production. In raw material and fuel there are many pollutants which are released by the pyro process. Switching to alternative fuels with biomass reduces carbon dioxide emissions, but in turn typically increases the chlorine input and the risk of blockages in the cyclones.
To ensure that the preheater functions without restrictions, a bypass system extracts up to 60% of the process gas. This removes gas components that disturb the process from the pyro process. This gas stream is later fed back into the process where the raw meal is added. In a normal operation, Norcem operates the bypass with less than 10% of the exhaust gas volume.
Fabric filters are a particularly efficient and frequently used filter technology. The dust-laden flue gas flows into the filter chamber and passes through several filter bags. The coarse particles fall by gravity and the fine particles accumulate on the surface of the permeable filter and form a layer of dust, usually called filter cake. Compressed air periodically cleans this filter cake but over time, small holes can form in the fabric. As a result, the gas enters the exhaust air unfiltered and worsens the emission limits.
Measuring dust made easy
To prevent this from happening the DUSTHUNTER SB30 measures after the material has been filtered and reports in real time, signaling when filters are damaged. The scattered light measuring principle − in this case with backward scattering − monitors constantly and is not influenced by the flow speed or the dust particle charge. This is an important advantage over other measuring methods, such as the triboelectric principle.
The self-monitoring function is particularly user-friendly because automatic test cycles reduce maintenance requirements and ensure that processes run smoothly. Norcem Kjøpsvik found installation and commissioning to be effortless. The dust measuring device was mounted on the exhaust duct on one side only making the additional effort for special alignments — as required for cross-channel transmission dust analyzers — eliminated. This DUSTHUNTER SB30 has no measuring probe, guaranteeing a longer instrument life because aggressive gases would attack a probe, causing corrosion and abrasion.
The significantly higher detection sensitivity of the DUSTHUNTER SB30 combined with the cost-effective installation and maintenance makes this product work well in cement production plants.
The efficiency and profitability of the plant in Kjøpsvik has increased significantly – not only at the heat exchanger, but in the entire exhaust gas cleaning system. SICK had previously supplied gas analyzers for the rotary kiln of Norcem Kjøpsvik and out of conviction, Norcem decided to use dust measurement technology from SICK.
“Regarding the dust analyzers, there is not much to say. We oversee the equipment every fourth week, and we haven’t had a single problem since we installed them,” said Erik Nilsen, Maintenance Manager at NORCEM.
Want to learn more about dust analyzer and reducing emissions? Contact a SICK representative today!